CH. IX] DIVERGENCE OF VARIATION 81 



or three largest genera in the family. Of course, since we cannot 

 be sure of what is the largest divergence, nor be sure that that 

 divergence necessarily came first in the mutations, we shall not 

 expect every family to show such a result with any certainty, 

 though one may expect it to show more often than not. The im- 

 portant point is that each sub-group should be headed by a com- 

 paratively large genus. If the group be small in proportion to the 

 family, the genus may be small in proportion to some of the 

 largest genera of the family ; if large, one will expect its leading 

 genus to be larger. 



We shall further expect to find the smaller genera practically 

 all included in the key that is marked out by the first divergent 

 mutation. That is to say, that we shall in general expect them to 

 be grouped as satellites round the big genera, not. as one might 

 expect if they were relics, in small and comparatively isolated 

 groups, which need not necessarily be closely related to the big 

 groups of the present day. We shall, therefore, expect the charac- 

 ters of these small genera to be less and less marked the smaller 

 (by the number of species in them) that they are, and to be, so to 

 speak, squeezed in between the well-marked characters of the 

 large genera. Real relics, on the other hand, would be more likely 

 to be distinguished fairly clearly from their relatives of the same 

 familv, bv characters that might even be as marked as those that 

 show in the first or second dichotomy of the key. 



The Ranunculaceae, a family of medium size, not very much 

 larger than the average size for all families, have seven genera 

 that (in comparison with the rest of the family) we may call 

 large, each one containing at least seventy-five species. There are 

 nine of intermediate size with ten or more, but none exceeding 

 twenty (figures some years old), and ten small with nine or less. 

 This gap between the large and the intermediate genera is not an 

 uncommon occurrence, especially in families of small and medium 

 size, and should be well worth further investigation. 



The big genera are : 



Total 1180 or 87 per cent of the family 



WED 



